Hot drawing tubes



Dec. 27, 1966 EDGECOMBE ETAL 3,293,894

HOT DRAWING TUBES Filed May 28, 1964 3 Sheets-Sheet 1 FIG! FURNACE 33 Ga: 7m A W INVENTORS David A. Ed ecombe Howar d W. arshall BY SIdIey 0.Evans Dec. 27, 1966 D. A. EDGECOMBE ETAL HOT DRAWING TUBES 3Sheets-Sheet 2 Filed May 28, 1964 fi R W n H r J? rm o mm w vdI .EDGECOMBE ETAL HOT DRAWING TUBES Dec. 27, 1966 3 Sheets-Sheet 5 FiledMay 23, 1964.

United States Patent M 3,293,894 HOT DRAWING TUBES David A. Edgecornbe,Howard W. Marshall, and Sidley 0.

Evans, all of Beaver Falls, Pa., assignors to The Babcock & WilcoxCompany, New York, N.Y., a corporation of New Jersey Filed May 23, 1964,Ser. No. 370,851

- 6 Claims. (CI. 72-42) This invention relates to the deformation ofmetals, and particularly to the hot plug mandrel drawing of ferrousmetal tubes.

In the tube production field many procedures are used to obtain thedesired tube diameter and wall thickness in particular metalcompositions. The tube may be extruded or pierced to the generallydesired dimensions, but ordinarily the extruded or rotary pierced tubemust be further worked to attain the desired dimensions and surfacefinish. Such working may be by cold working although some ferrous metalcompositions are diflicult or even impossible to cold work. Some workingmay be by hot processes where the tube is heated to a plastic orsemiplastic condition prior to working.

In any drawing procedure, whether hot or cold the tube must be clean andscale free. Also, in both, the percentage reduction each drawing pass isrestricted to avoid tube failure by necking or rupture. In coldreduction it is desirable to anneal, clean and relubricate the tubebefore each reduction pass, while in hot reducing it is frequentlypossible to make two or more drawing passes of a tube without anintermediate reheat. Even with reheating, tube preparation for hotdrawing of stainless steels is limited to an additional relativelysimple application of lubricating material such as glass prior to eachpass through the reducing die. Thus, in many instances hot drawing oftubes is more economical and the finished tube may be particularlydesirable for some uses.

The various features of novelty which characterize our invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which we have illustrated and described a preferred embodimentof the invention.

Of the drawings:

FIG. 1 is a schematic plan of a draw bench with a die, arranged with afurnace to illustrate an arrangement suitable to perform the presentinvention;

FIG. 2 is a large scale elevation, in section showing the relationshipof a tube, die and plug mandrel when hot reducing a tube with a glasslubricant; and

3,293,594 Patented Dec. 27, I966 As shown, the die 13 has a convergingtapered entrance 21 and a diverging tapered exit 22, both offrusto-conical form. The die is mounted in well known manner for readyreplacement of the die for changes in the desired diameter of the tubeor for any other reason.

In the hot drawing procedure of this invention a mandrel or plug 23 ismounted on the end of a shaft or rod 24 which is longitudinallyadjustable relative to the die 13 so that the mandrel 23 may bepositioned within the tube 11 for proper coordination of the drawingoperation. The mandrel 23 illustrated is generally cylindrical in shapeand may have an integral end portion 25 of reduced diameter. Theconstruction shown aids in the initial axial positioning of the mandrel,during the beginning of the tube drawing operation. In starting, themandrel 23 is advanced with the tube 11 for the beginning of the outsidediameter reduction, and as the tube is drawn through the die the mandrelwill be advanced into the throat of the die 13. The internal shape ofthe tube will then be as indicated at 25' in FIG. 2 where the shoulderend portion 25 will also usually be indicated by an impression 26'.

Before any tube drawing can occur the tube must be at a desirabletemperature which is dependent upon the composition of the tube metal.Generally the temperature range for ferrous tubes will be from 1500 to2200 F. with a temperature of 1500 to 1900 F. for stainless steel, forexample. We have found that a layer of glass lubricant must be appliedto the tube surfaces before the tube is drawn to reduce the frictionbetween the tube 11 and the work tools, i.e. the die 13 and the mandrel23. The lubricant may be applied to the tube when the tube is attemperature or slightly below the desired working tem perature. If atthe latter temperature, the heating will be resumed after the glasslubricant has been applied to the tube.

With the desirable working temperature of the tube dependent upon thecomposition of the tube metal, the composition of the glass used as alubricant will also vary with the metal of the tube to be worked. Thelubricant desirably will coat the surface of the metal upon contactingthe hot tube, while still retaining sufficient body or having aviscosity adequate to form a thin protective film between the tool andthe workpiece. A suitable glass for the lubrication of stainless steeltubes heated to aworking temperature of the order of 1900 F. has thefollowing composition:

Percent Na O 37.5

FIGS. 3 to 6 show schematically a typical sequence of operations of adraw bench constructed, arranged and operated in accordance with thepresent invention.

As shown in the drawings, the equipment arrangement illustrates afurnace 10 positionedat one side of the draw bench 12, so that theheated tube 11 may be transferred from the furnace to the draw benchwith a minimum loss of tube heat. It will be understood the furnace canbe located above or below, on either side, or in alignment with the drawbench, as desired in any particular installation.

In the usual draw bench arrangement a die 13 is mount ed in a fixedlocation relative to the moving head or car.- riage 14 which moves onrails 15. The carriage 14 is mounted on wheels 16 and is positivelydriven along the rails 15, as for example by a hook (not shown) attachedto the carriage and engaging an endless chain 17 operable between therails 15. The carriage is provided with jaws 18 (indicated in FIG. 2)operable to engage the swaged or pointed end 20 of the tube 11.

Another glass suitable for the purposes has a lower SiO and Na Ocontent, but a higher B 0 content. This glass may also contain smallpercentages of aluminum, iron andcalcium oxides.

In applying the lubricating glass to the tube, the glass may be in anydesirable form. For example, we have found that dipping the tube in amolten tank of glass-like material or a powdered glass is convenient,and either can be easily handled and applied. When powdered glass isused, the outside diameter of the tube will be coated with sufficientlubricant to protect the exterior surface while the tube is being drawn.This is illustrated in FIG. 2, where the glass lubricant 30 accumulatesbetween the face 31 of the die 13 and the exterior surf face of the tube11. It is advantageous to coat the entire exterior surface of the tube,as can be accomplished by sprinkling powdered glass from a vibratinghopper.

die 13.

of glass lubricant for the inside surface of the drawn or reduced tube.Lubricating glass distribution to the inside of the tube 11 can beattained by flowing the glass powder in a transporting gas stream intothe tube. The glass powder may also be introduced by a spoon or channel,or the like, along the bottom of the tubewith the tube being rotated forcircumferential distribution of the glass. Any excess of glasslubricant, in either solid or liquid form, will be rolled back orskimmed-01f by the action of the mandrel 23 to provide an accumulation33 similar to the accumulation 30 on the exterior surface of the tube.

In drawing a tube 11 through the die 13 and over the mandrel 23, thetube may be at temperature of 1950 F. and fully coated with lubricatingglass, and while the drawing operation may start at a slow rate untilthe mandrel is set in proper position relative to the die, the drawingrate will thereafter be accelerated to a high rate. The drawing ratewill usually be at least triple the possible rate for a correspondingcold reduction. Maintaining the high drawing rate protects tools fromoverheating and of course provides fast and economic operation.

We have found it desirable to preheat both the die and the mandrel priorto starting the drawing operation, so as to limit the cooling effect oftube contact with the die and the mandrel. A suitable preheattemperature will be 300 to 400 F. For the same reasons we have found itdesirable to use a rod 24 of minimum crosssection consistent withstrength requirements and to polish the exterior surface of the rod 24to refiect radiant heat therefrom.

On occasion we have also found it desirable to cool and sometimes toactually quench the drawn tube closely downstream, in a tube drawingsense, of the die to strengthen the tube, so as to avoid necking or evenrupturing the tube adjacent the die. A manifold 19 is shown in FIG. 2for this purpose. Such conditions usually arise with a tube drawing areareduction in excess of 30%.

While it is possible to hold the plug mandrel 23 in the same positionrelative to the die 13 throughout the period of tube drawing, and stillproduce a tube finished to close dimensional tolerance and havingdesirable surfaces under the procedures hereinbefore described, theuseful life of the plug mandrel is usually limited to the drawing of6-12 tubes. On the other hand if the plug mandrel is controllably movedthe useful life of the mandrel is of the order of 50-100 tube drawingcycles.

From a commercial standpoint we have found it desirable to positivelydrive or to permit controlled longitudinal movement of the plug mandrel23 during the tube drawing process so as to reduce the damage to andwear on the plug mandrel 23. The positive controlled movement of themandrel during the tube drawing cycle can be attained by mechanicalmeans including a motor driven screw or a gear connection with themechanism driving the carriage 14, or particularly in installation fordrawing tubes of relatively large dimensions a hydraulic mechanism canbe used. A suitable hydraulic system for the purpose is shown in FIGS. 3to 6, inclusive.

As shown, the plug mandrel 23 and rod 24 are positioned by a long strokepiston 35 operable in a cylinder 36. In FIG. 3, the plug mandrel 23 isshown in its retracted position so that the tube 11 may be positioned inlongitudinal alignment with the die 13. The flow of hydraulic fluid froma pressure source (not shown) through a connecting pipe 37 to thecylinder 36 is regulated by a conventional flow control device indicatedgenerally at 38. The flow control device may be electrically actuated bya push button or the like to advance from the position of the mandrelshown in FIG. 3 to the position shown in FIG. 4, where the advance tothe position shown in the latter view is limited by contact with a limitswitch 40.

In FIG. 4, the tube 11 has been advanced with its neck portion 20 pushedthrough the die 13 to be gripped by the jaws 18 of the carriage 14. .Themovement of the tube is independent of mandrel movement, and while thetube and mandrel advance may be simultaneous to the position shown inFIG. 4, the advances need not be simultaneous.

With the start of the drawing operation, the carriage 14 will move awayfrom the die 13 and at the same time the mandrel 23 will set within thetube 11 and within the die. The start of the carriage movement willeither automatically or manually further advance the mandrel to theposition shown in FIG. 5. The mandrel 23 is slowly advanced during thetube draw, where the advance will be controlled in an amount of 2 to 7inches, so as to avoid localized overheating of the mandrel.

The mandrel 23 advance is regulated by bleeding hydraulic fiuid from apair of hydraulic cylinders 41 and 42 through a flow control valve 43into a pressurized accumulator 44. The valve 43 is controlled toregulate the rate of hydraulic fluid movement therethrough so that themovement of pistons 45 and 46 in the cylinders 41 and 42, respectively,permits a corresponding movement of an elongated hollow element 47. Theelement 47 is connected to and supported by a yoke 48 on the piston rodsof the pistons 45 and 46 so that movement of the element 47 by reason ofa movement of a collar 50 bearing on an end wall of the element aseffected by piston 35 is limited in rate and length by the fluid flowthrough the valve 43.

At the end of the tube drawing operation the mandrel 23 will be advancedto the position shown in FIG. 6. Thereafter the drawn tube is removed,and the mandrel retracted to the position shown in FIG. 3, for the nexttube drawing cycle.

By way of example and not of limitation hot stainless steel tubes weredrawn according to our invention as shown in the following table:

EXPERIMENT #14 Percent Percent Total Area Reduction Red.

EXPERIMENT #4 end EXPERIMENT #5 Start 3. 500 2. 966

EXPERIMENT #6 Start end...

EXPE RIMENT #7 Start--. end

EXPERIMENT #26 1 Outside Dimension. 2 Hot Dimension. 6 Cold Dimension.

The hot drawing procedure of the :present invention is particularlyuseful in the drawing of tubes, but can be usefully applied in the areareduction of other shapes. Tubes finished by hot reduction have hadexceptional surfaces, and the dimensional control has been well withincommercial tolerances. It has also been found to produce finished tubesof either large and small diameters, and there is no known limit ondiameter to wall ratios.

While in accordance with the provisions of the statutes we haveillustrated and described herein the best form and mode of operation ofthe invention now known to us, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by our claims, andthat certain features of our invention may sometimes be used toadvantage without a corresponding use of other features.

What is claimed is:

1. The method of drawing a ferrous metal workpiece through a die tochange the cross-section of the workpiece which comprises the steps ofheating the workpiece to a temperature in the range of 1500 to 2200" F.,applying a layer of glass-like lubricant to the surface of said hotworkpiece, said glass-like lubricant being viscous at the heatedtemperature, and drawing said hot lubricated workpiece to change thecross-section thereof with the viscous glass-like lubricant protectingthe surfaces of the workpiece during drawing.

2. The method of hot drawing wherein a tube is drawn through a die andover a mandrel to change the crosssection of the tube which comprisesthe steps of heating the tube to a temperature in the range of 1500 to2200 F., applying a layer of glass-like lubricant to the inner and outersurfaces of said hot tube, said glass-like lubricant being viscous atthe heated temperature, and drawing said hot lubricated tube to changethe cross-section thereof with the viscous glass-like lubricantprotecting the surfaces of the tube during drawing.

3. The method of hot drawing wherein a stainless steel tube is drawnthrough a die and over a mandrel to change the cross-section of the tubewhich comprises the steps of heating the tube to a temperature in therange of 1500 to 1900 F., applying a layer of glass-like lubricant tothe inner and outer surfaces of said tube, said glass-like lubricantbeing viscous at the heated temperature, and drawing said hot lubricatedtube to change the crosssection thereof with the viscous glass-likelubricant protecting the surfaces of the tube during drawing.

4-. The method of drawing a ferrous metal tube through a die and over amandrel to change the cross-section of the tube which comprises thesteps of heating the tube to a temperature in the range of 1500 to 2200F., preheating the die and mandrel to a temperature of the order of 400F, applying a layer of glass-like lubricant to the surfaces of saidtube, said glass-like lubricant being viscous at the heated temperature,and drawing said hot lubricated tube to change the cross-section thereofwith the viscous glass-like lubricant rotecting the surfaces of the tubeand die and mandrel during drawing.

5. The method of drawing a ferrous metal tube through a die and over amandrel to change the cross-section of the tube which comprises thesteps of heating the tube to a temperature in the range of 1500 to 2200F., applying a layer of glass-like lubricant to the surfaces of said hottube, said glass-like lubricant being viscous at the heated temperature,drawing said hot lubricated tube to change the cross-section thereofwith the viscous glass-like lubricant protecting the surfaces of thetube during drawing, and moving the mandrel relative to the die whilethe tube is being drawn through the die and over the mandrel.

6. The method of hot drawing wherein a tube is drawn through a die andover a mandrel to change the crosssection of the tube which comprisesthe steps of heating the tube to a temperature in the range of 1500 to2200 F, applying a layer of glass-like lubricant to the inner and outersurfaces of said tube, said glass-like lubricant being viscous at theheated temperature of the tube, preheating the die and mandrel to atemperature of the order of 400 F, drawing said hot lubricated tube tochange the cross-section thereof with the viscous glass-like lubricantprotecting the surfaces of the tube during drawing, and quenching thedrawn tube leaving the die to avoid ruptur ing of the tube.

References Cited by the Examiner UNITED STATES PATENTS 537,454 4/1895Hewlett 72-286 2,067,530 1/1937 Ihrig 205-211 2,285,539 6/1942 Stapleset a1 72283 2,351,710 6/1944 Sanders 72283 2,390,644 12/1945 Diehn205-2l.l 3,021,941 2/1962 Huet 20521.1 3,039,888 6/1962 Sejournet et al7242 CHARLES W. LANHAM, Primary Examiner.

H. D. HOINKES, Assistant Examiner.

1. THE METHOD OF DRAWING A FERROUS METAL WORKPIECE THROUGH A DIE TOCHANGE THE CROSS-SECTION OF THE WORKPIECE WHICH COMPRISES THE STEPS OFHEATING THE WORKPIECE TEMPERATURE IN THE RANGE OF 1500 TO 2200*F.,APPLYING A LAYER OF GLASS-LIKE LUBRICANT TO THE SURFACE OF SAID HOTWORKPIECE, SAID GLASS-LIKE LUBRICANT BEING VISCOUS AT THE HEATEDTEMPERATURE, AND DRAWING SAID HOT LUBRICATED WORKPIECE TO CHENGE THECROSS-SECTION THEREOF WITH THE VISCOUS GLASS-LIKE LUBRICANT PROJECTINGTHE SURFACE OF THE WORKPIECE DURING DRAWING.